Golf balls are made in a variety of constructions and compositions. Generally, a core is surrounded by a cover, with at least one intermediate layer optionally disposed there between. Examples of conventional golf ball materials range from balata to polybutadiene, ionomer resins, polyurethanes, and/or polyureas. Typically, outer layers are formed about the spherical outer surface of an inner golf ball component via compression molding, casting, or injection molding.
Golf ball manufacturers continuously experiment with constructions and material formulations in order to target and improve aerodynamic and/or inertial properties and achieve desired feel without sacrificing durability. In this regard, thermoplastic ionomers and/or castable polyurethanes/ureas are popular cover materials, and ionomer blends are often used as casing materials. Balata, meanwhile, was popular at one point as providing desirable feel and control.
While each of these materials can impart desirable attributes to the cover, certain attendant limitations/drawbacks thereto are also known. For example, ionomer-based cover formulations can favorably impart excellent shear and abrasion resistance, but typically need to have a Shore D hardness greater than 60 to deliver those exceptional shear ratings. Unfortunately, such high cover hardnesses tend to lack the “feel” and “control” that many golfers desire—offering the golfer little in terms of delivering backspin with the short irons. Meanwhile, castable/injection moldable polyurethane/polyurea formulations can impart exceptional feel at lower hardnesses and exhibit excellent shear/abrasion resistance, but don't typically lend themselves to partial adjustment of the formulation during processing, for example, to change the cure package. And balata covered golf balls undesirably tend to exhibit poor shear/abrasion resistance and are expensive and difficult to produce.
One manufacturer blended conventional polybutadiene rubber with polyurethane rubber and optionally balata in relative amounts of 10-60% polybutadiene rubber, 10-90% polyether/polyester based millable polyurethane rubber, and 0-50% polyisoprene using a typical rubber making process. Golf balls were produced having a feel, resilience, flight properties and/or spin rate comparable to competitive polyurethane covered golf balls that differed therefrom with regard to the cover material as well as in other respects. See, U.S. Pat. No. 6,152,836 to Bradley et al. (“Bradley”) at TABLES 1, 2 and 3 (Titleist Professional or Maxfli Revolution).
There is thus still a need for golf balls having layers/covers that can be interchanged with conventional polyurethane layer/cover materials without the need to otherwise modify the golf ball's construction and yet can be formed within a flexible process that permits partial adjustment of the layer/cover formulation during processing without including conventional polybutadiene rubber. The present inventive golf balls and methods of making such golf balls address and solve this need.